1. Field of the Invention
The invention relates to a pH-sensor based on fiber optics. More specifically, the invention is directed to the chemical modification of the poly (methyl methacrylate) clad surface of an optical fiber to introduce amino groups, and thereafter, binding a pH sensitive dye to the clad surface.
2. Description of the Prior Art
Functional polymers find numerous applications as supports in solid phase synthesis, as discussed by R. B. Merrifield, J. Amer. Chem. Soc., 85, 2149 (1963); in reagents, as discussed by P. Hodge and D. C. Sherrington, Eds., "Polymer Supported Reactions in Organic Synthesis", John Wiley, New York, 1980: in Chromatography as discussed by J. M. J. Fretchet, A. J. Hagen, C. Benezra, and A. Cheminat, Pure Appl. Chem., Volume 54, 2181 (1982); and in catalysts as discussed by C. U. Pittman and G. Evans, Chem. Tech., 560 (1973).
There are two general methods for introducing functional groups into polymers. First, by polymerization of the corresponding monomers and second, by chemical modification of the preformed polymers. For introducing functional groups on surfaces, only the latter method is suitable. The most widely studied chemical modification reaction of poly(methyl methacrylate) (PMMA) has been hydrolysis to poly(methacrylic acid), while research on introducing other functionalities in PMMA has received much less attention.
This subject is discussed by L. Feistel, D. Krauss, and G. Schwachula in Ger. Patent No. 212,258 (1984); by A. Akelah, M. Hassanein, A. Selim, and E. R. Keanwy in Polym. Prep., Vol. 27 (1), 468 (1986); and by V. M. Balankin, A. G. Tesler, and V. S. Talankin, Vysokomol, Soedin, Ser. B., Vol. 26, 384 (1984). In the work of the invention on the development of a pH sensor based on fiber optics, it was of considerable interest to chemically modify the surface of the PMMA cladding of an optical fiber to introduce amino groups. A pH-sensitive dye with isothiocyanate functionality, which has been developed in the invention, would then be bound on the optical fiber utilizing the amino groups located at the surface of the fiber. Reactions between isothiocyanates and primary amines are very fast and should be completed in a relatively short time even under heterogeneous conditions. A literature review revealed that procedures used previously in aminolysis of esters were unsuitable, because they either employed solvents that would dissolve the fiber or employed temperature conditions that would destroy the fiber.